Downhole gas lift pipe column and method

Abstract

The invention belongs to the field of petroleum and natural gas extraction, and particularly relates to an underground gas lift pipe column and method. The pipe column comprises an oil pipe, a packing part, an intelligent control valve and a sliding sleeve selectively arranged on the oil pipe. The packing part participates in packing operation of the gas source section and comprises at least one packer. The intelligent control valve is connected to the oil pipe and located in the gas source section. The intelligent control valve is constructed to enable high-pressure gas in the gas source section to enter the oil pipe to lift accumulated liquid in a shaft out of the shaft when the intelligent control valve is in an open state. Effective drainage of accumulated liquid in the shaft can be realized by utilizing the gas source section in the water accumulation shaft, so that the cost and energy consumption of a gas lift process are reduced, and the device has a good application prospect in the field.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of oil and gas exploitation, and particularly relates to a downhole gas lift string and method. BACKGROUND

[0002] Once a natural gas well produces water, the wellbore pressure loss will be increased, and the gas production will be reduced. At present, the drainage gas recovery technology is mainly used to maintain the stable production of the water-producing gas well. For the well with large liquid production, the drainage gas recovery technologies such as foam drainage and plunger cannot meet the strength requirement of drainage and production, and generally need to use external high-pressure gas source, usually natural gas or nitrogen, to inject into the annulus, lift the well bottom liquid out of the wellhead through the tubing bottom boundary, and then release the gas well production capacity. The operation modes generally include the following modes:

[0003] (1) Natural gas vehicle gas lift: a vehicle-mounted compressor is needed to take natural gas from the station process, the natural gas is pressurized by the vehicle-mounted compressor and then injected into the annulus of the gas well, the well bottom liquid is lifted out of the wellhead through the tubing bottom boundary, and is used for temporary gas lift and production recovery.

[0004] (2) Membrane nitrogen gas lift: an air nitrogen preparation vehicle and a pump truck are needed, the prepared nitrogen is pumped into the annulus of the gas well by the pump truck, the well bottom liquid is lifted out of the wellhead through the tubing bottom boundary, and is used for temporary gas lift and production recovery.

[0005] (3) Tank truck gas lift: a tank truck is needed to take compressed natural gas as a high-pressure gas source to inject into the annulus of the gas well, the well bottom liquid is lifted out of the wellhead through the tubing bottom boundary, and is used for temporary gas lift and production recovery.

[0006] (4) Interwell gas lift: a gas lift process is built between the wells in the same well station to connect the annuli of the wells, and the high-pressure well is used as a gas source to lift the remaining wells.

[0007] (5) Continuous gas lift: a skid-mounted compressor is needed to take the pipeline network gas, the gas is pressurized by the compressor and then injected into the annulus of the gas well, the well bottom liquid is lifted out of the wellhead through the tubing bottom boundary, and is used for continuous gas lift and production maintenance.

[0008] These gas lift modes need to use external energy, and need to additionally provide gas lift equipment or build a gas lift process, the operation cost is high, and the membrane nitrogen gas lift mode cannot realize continuous gas lift and can only be used for temporary production recovery.

[0009] Therefore, how to reduce the cost of gas lift and drainage, and improve the flexibility of gas lift operation and the convenience of gas lift control has become a technical problem to be solved. SUMMARY

[0010] In view of part or all of the problems in the prior art, the present application provides a downhole gas lift string and method.

[0011] According to a first aspect of the present application, a downhole gas lift string is provided.

[0012] The downhole gas lift string comprises:

[0013] A tubing;

[0014] A packoff section participating in packoff operation of the gas source section, comprising no less than one packer;

[0015] An intelligent control valve configured to be connected to the tubing and located in the gas source section; and

[0016] A sliding sleeve selectively arranged on the tubing,

[0017] Wherein, the intelligent control valve is configured to, in an open state, enable high-pressure gas in the gas source section to enter the tubing to lift accumulated liquid inside the wellbore out of the well.

[0018] As an extension of the above technical solution, the present application further provides the following embodiments:

[0019] The intelligent control valve comprises a first body, a first circulation hole opened on the side wall of the first body, and a gas guide cylinder arranged inside the first body, a control assembly configured to be able to operate in response to an external instruction is arranged inside the gas guide cylinder, and an extension mechanism is connected above the control assembly, the extension mechanism is configured to be able to move to block or expose the circulation hole in response to the instruction of the control assembly.

[0020] The control assembly comprises a sealing cylinder, and a control power supply, a motor and a transmission mechanism assembled inside the sealing cylinder, the control power supply is configured to be able to realize connection and communication with the issuing device of the external instruction, and successively cause the motor and the transmission mechanism to operate, the transmission mechanism is configured to be able to drive the extension mechanism to move.

[0021] For a horizontal well, an inclined well or a vertical well in which the gas source section is located at the uppermost section of the wellbore, the packoff section comprises a first packer, and the gas source section is sealed by the first packer and a wellhead device.

[0022] For a horizontal well, an inclined well or a vertical well in which the gas source section is located at the middle section of the wellbore, the packoff section comprises the first packer and a second packer, and the gas source section is sealed by the first packer and the second packer, and a sliding sleeve is arranged on the tubing close to the wellhead side of the packoff section.

[0023] The pack-off part comprises the first packer, the smart control valve is arranged at the lowermost end of the tubing, and a plug configured to close the lower end of the tubing is arranged at the lower end of the smart control valve, and a sliding sleeve is arranged on the tubing close to the wellhead side of the pack-off part.

[0024] The surface control part is configured to control the opening and closing of the smart control valve.

[0025] The surface control part comprises a control host, a first pressure measuring pipeline and a second pressure measuring pipeline respectively extending from the control host to the inside of the tubing and the annulus between the tubing and the wellbore, and a cable connecting the control host and the smart control valve, and the control host is configured to automatically control the smart control valve to be in an open or closed state by calculating and judging the pressure data fed back by the first pressure measuring pipeline and the second pressure measuring pipeline.

[0026] According to a second aspect of the present application, a downhole gas lifting method is provided.

[0027] The downhole gas lifting method is performed by using the downhole gas lifting string as described above, and comprises the following steps:

[0028] 1) judging the liquid accumulation in the wellbore;

[0029] 2) when the liquid accumulation in the wellbore reaches or exceeds a set opening threshold, opening the smart control valve and performing gas lifting operation by using the gas source section;

[0030] 3) when the liquid accumulation in the wellbore decreases to or below a set closing threshold, closing the smart control valve and ending the gas lifting operation.

[0031] As an extension of the above technical solution, the present application further provides the following embodiments:

[0032] In the step 1), the calculation equation for judging the liquid accumulation in the wellbore is: W=3.14*10 -6 *d 2 *(Pc-Pt) / 4ρg, wherein W represents the calculated liquid accumulation in the wellbore, d represents the inner diameter of the tubing, Pc represents the pressure in the annulus, Pt represents the pressure in the tubing, ρ represents the density of the liquid accumulation in the wellbore, and g represents the acceleration of gravity.

[0033] The present application has the following advantages compared with the prior art:

[0034] Firstly, by the design and application of the downhole gas lift string, the gas accumulation wellbore can use the gas source section as a gas source to complete the gas lift operation, without the need to increase additional gas source, gas lift equipment and process, thereby reducing the cost and energy consumption of the gas lift operation and improving the efficiency of the gas lift operation.

[0035] Secondly, by the design and cooperation of the intelligent control valve and the control part, the automatic judgment of the downhole gas accumulation condition and the automatic operation of the gas lift operation are realized, and the flexibility, automation level and operation convenience of the gas lift operation are improved.

[0036] Thirdly, thanks to the design and use of the sealing part, the gas source section is isolated from other gas production sections, and the interference between different sections is avoided, so that the gas lift operation is smoothly realized without obvious influence on the gas production.

[0037] In addition, the technical scheme provided by the present application can be applied to various types of wells such as horizontal wells, inclined wells and straight wells, and various working conditions where the gas source section is located at different positions in the well, and the application range is wide. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a structural schematic view of one embodiment of the downhole gas lift string according to the present application;

[0039] Figure 2 is a structural schematic view of another embodiment of the downhole gas lift string according to the present application;

[0040] Figure 3 is a structural schematic view of a third embodiment of the downhole gas lift string according to the present application;

[0041] Figure 4 is a structural schematic view of a fourth embodiment of the downhole gas lift string according to the present application;

[0042] Figure 5 is a structural schematic view of the intelligent control valve according to the present application;

[0043] Figure 6 is a structural schematic view of the sliding sleeve according to the present application.

[0044] All the drawings in the present application are schematic views for illustrating the structure and principle, and are not necessarily drawn according to the actual size and proportion.

[0045] The specific meanings of various reference signs in the drawings are as follows:

[0046] 1, tubing; 2, pack-off section; 21, first packer; 22, second packer; 3, intelligent control valve; 31, first body; 32, first circulation hole; 33, gas guide cylinder; 34, control assembly; 341, sealing cylinder; 342, control power supply; 343, motor; 344, transmission mechanism; 35, telescopic mechanism; 36, first external thread; 37, first internal thread; 4, sliding sleeve; 41, second body; 42, second circulation hole; 43, second external thread; 44, second internal thread; 5, wellbore; 51, gas source section; 6, surface control section; 61, control host; 62, first pressure measurement pipeline; 63, second pressure measurement pipeline; 100, downhole gas lift string. DETAILED DESCRIPTION

[0047] The embodiments of the present application will be described in more detail below with reference to the accompanying drawings.

[0048] First of all, it needs to be pointed out that in the present application, the section in the wellbore 5 selected to provide high-pressure gas for gas lift operation is defined as the gas source section 51.

[0049] According to a first aspect of the present application, a downhole gas lift string 100 is provided.

[0050] Figures 1 to 4 A structural schematic diagram of the downhole gas lift string 100 according to the present application (hereinafter referred to as "string 100") is shown in the figure. As shown in the figure, the string 100 includes a tubing 1, a pack-off section 2, an intelligent control valve 3, and a sliding sleeve 4 selectively arranged on the tubing 1. The pack-off section 2 is arranged on the outside of the tubing 1 and participates in the pack-off operation to isolate the gas source section 51 from other sections in the wellbore 5, which includes no less than one packer. The intelligent control valve 3 is configured to be connected to the tubing 1 and located in the area where the gas source section 51 is located. Moreover, the intelligent control valve 3 is also configured not to affect the flow state of the gas inside the tubing 1, and in the closed state, it can store the gas in the gas source section 51, and in the open state, it can make the high-pressure gas in the gas source section 51 enter the tubing 1 to lift the accumulated liquid inside the wellbore 5 out of the well, thereby completing the gas lift operation.

[0051] In the specific operation, the staff sets the applicable pipe string 100 in the wellbore 5 according to the actual well condition. In the normal production operation, the intelligent control valve 3 is in the closed state, so that the high-pressure gas in the gas source section 51 is stored by itself and the packer 2. The gas in other gas production sections in the wellbore 5 is produced by entering the oil pipe 1 through the bottom boundary of the oil pipe 1 or entering the oil pipe through the sliding sleeve 4 arranged on the oil pipe 1. After a period of production, it is judged that gas lifting operation is needed, and the staff opens the intelligent control valve 3, at this time the high-pressure gas in the gas source section 51 enters the oil pipe 1 through the intelligent control valve 3 to carry out gas lifting operation. When the accumulated liquid in the wellbore 5 is discharged to a certain limit, the staff can close the intelligent control valve 3 to continue the production operation of the wellbore 5.

[0052] Through this design, the wellbore 5 with the problem of accumulated liquid can use its own gas source section 51 as a gas source to complete the gas lifting operation, without the need to increase additional gas source, gas lifting equipment and process, thereby reducing the cost and energy consumption of the gas lifting operation, and improving the efficiency of the gas lifting operation. In addition, thanks to the design and use of the packer 2, the isolation between the gas source section 51 and other gas production sections is realized in the normal production stage, avoiding the interference between different sections, so that the gas lifting operation is smoothly realized without obvious influence on the gas production.

[0053] As shown in Figure 5 In one embodiment of the present application, the intelligent control valve 3 includes a first body 31, a first circulation hole 32, a gas guide cylinder 33, a control assembly 34 and an extension mechanism 35. The first body 31 is configured as a hollow tubular structure, and a plurality of first circulation holes 32 are formed in the side wall of the first body 31 to facilitate the high-pressure gas in the gas source section 51 to enter the inside of the oil pipe 1. The inside of the first body 31 is provided with a gas guide cylinder 33 for guiding the gas in the oil pipe 1 to pass through the intelligent control valve 3. The inside of the gas guide cylinder 33 is provided with a control assembly 34 configured to operate in response to an external instruction, and the extension mechanism 35 is connected above the control assembly 34, which is configured to move in response to the instruction of the control assembly 33 to block or expose the circulation hole 32, so as to realize the opening or closing of the intelligent control valve 3. Through this design, the structure of the intelligent control valve 3 is clear, and the intelligent control valve 3 also has the advantages of convenient operation and flexible action, and can well realize the gas lifting function of the pipe string 100 after being applied.

[0054] Further, in one embodiment of the present application, the control assembly 34 comprises a sealing cylinder 341 and a control power supply 342, a motor 343 and a transmission mechanism 344 assembled inside the sealing cylinder 341. The sealing cylinder 341 constitutes a protective outer shell of the control assembly 34. The control power supply 342 is configured to supply power to the motor 343, and is further configured to be connected to and communicate with an external instruction issuing device. Thus, the control power supply 342 can control the operating state of the motor 343 according to the external instruction. The motor 343 drives the transmission mechanism 344 to operate by its own operation, and the transmission mechanism 344 is configured to drive the telescopic mechanism 35 to move to complete the opening or closing operation of the circulation hole 32. Through this design, the internal composition and working principle of the control assembly 34 are clear, and effective control of the operation of the intelligent control valve 3 is achieved. In addition, it should be noted that the sealing cylinder 341, the control power supply 342, the motor 343 and the transmission mechanism 344 can be any device or component that can achieve the functions in this embodiment in the prior art, and the specific structure and principle are well known to those skilled in the art, which will not be described here.

[0055] As shown in Figure 5 , in one embodiment of the present application, the intelligent control valve 3 comprises a first external thread 36 arranged on the outer side of the upper end of the first body 31, and a first internal thread 37 arranged on the inner side of the lower end of the first body 31. Through this design, the intelligent control valve 3 can be firmly connected with the oil pipe 1 through the first external thread 36 and the first internal thread 37, and the operation process is flexible and convenient.

[0056] As shown in Figure 6 , in some embodiments of the present application, the sliding sleeve 4 comprises a second body 41 configured as a hollow tubular structure and a second circulation hole 42 opened on the side wall of the second body 41. Through this design, the gas in the gas-producing layer section corresponding to the position of the sliding sleeve 4 can enter the inside of the sliding sleeve 4 through the second circulation hole 42 and then enter the inside of the oil pipe 1, which facilitates the oil and gas production operation.

[0057] Further, in one embodiment of the present application, the sliding sleeve 4 comprises a second external thread 43 arranged on the outer side of the upper end of the second body 41 and a second internal thread 44 arranged on the inner side of the lower end of the second body 41. Through this design, the sliding sleeve 4 can be firmly connected with the oil pipe 1 through the second external thread 43 and the second internal thread 44, and the operation process is flexible and convenient.

[0058] As shown in Figure 1As shown, in one embodiment of the present invention, a tubing string 100 is provided suitable for horizontal, deviated, or vertical wells, with the gas source section 51 located at the uppermost part of the wellbore 5. In the tubing string 100, the packer 2 includes a first packer 21, the gas source section 51 is sealed by the first packer 21 and the wellhead device, and the intelligent control valve 3 is connected to the tubing 1 and located within the gas source section 51. In this type of tubing string 100, a sliding sleeve 4 is not required on the tubing 1. Gas from the gas-producing zone enters the tubing 1 through the bottom boundary of the tubing 1 and is extracted.

[0059] like Figure 2 As shown, in one embodiment of the present invention, a tubing string 100 is provided suitable for horizontal, deviated, or vertical wells, with the gas source section 51 located in the middle section of the wellbore 5. In the tubing string 100, the packer 2 includes a first packer 21 and a second separator 22. The gas source section 51 is sealed by the first packer 21 and the second packer 22 to isolate it from other gas-producing sections. A smart control valve 3 is connected to the tubing 1 and located within the gas source section 51. A sliding sleeve 4 is provided on the tubing 1 near the wellhead of the sealing section 2 to facilitate the extraction of gas from the gas-producing section adjacent to the wellhead. Gas from other gas-producing sections in the wellbore 5 enters the tubing 1 through the bottom boundary of the tubing 1 and is extracted.

[0060] like Figure 3 and Figure 4 As shown, in one embodiment of the present invention, a tubing string 100 is provided, suitable for horizontal, deviated, or vertical wells, with the gas source section 51 located at the lowest point within the wellbore 1. In the tubing string 100, the packer 2 includes a first packer 21. Since the gas source section 51 is located at the lowest point of the wellbore 5, it is sealed off by the first packer 21 and the lower boundary of the wellbore 5, thus isolating it from other gas-producing sections within the wellbore 5. The lower end of the intelligent control valve 3, located within the gas source section 51, is also equipped with a plug (not shown, the same below) capable of sealing the lower end of the tubing 1 to prevent high-pressure gas in the gas source section 51 from entering the tubing 1 through the bottom boundary of the tubing 1. A sliding sleeve 4 is provided on the tubing 1 on the side of the packer 2 near the wellhead, through which gas from the gas-producing sections within the wellbore 1 enters the tubing 1 and is extracted.

[0061] like Figures 1 to 4 As shown, in some embodiments of the present invention, the tubing string 100 includes a surface control unit 6 configured to control the opening and closing of the intelligent control valve 3. This design allows operators to control the intelligent control valve 3 located downhole from the surface, thereby improving the convenience of operators operating the tubing string 100 for gas lift operations.

[0062] Further, in one embodiment of the present application, the surface control unit 6 comprises a control host 61, a first pressure measuring pipeline 62, a second pressure measuring pipeline 63 and a cable (not shown, same below). The control host 61 is arranged on the ground, the first pressure measuring pipeline 62 and the second pressure measuring pipeline 63 are respectively extended from the control host 61 to the inside of the tubing 1 and the annulus between the wellbore 5 and the tubing 1 to measure the pressure values and pressure changes of the tubing 1 and the annulus, respectively, and the cable is configured to connect the control host 61 with the smart valve 3. The control host 61 is further configured to determine the opening or closing state of the smart valve 3 by calculating the pressure data measured and fed back by the first pressure measuring pipeline 61 and the second pressure measuring pipeline 62 and sending instructions to the smart valve 3 through the cable. By this design, the pipe string 100 can automatically determine the liquid loading condition in the wellbore 5 and perform or end the gas lifting operation at the appropriate time, improving the flexibility, automation level and operation convenience of the gas lifting operation. It should be noted that the components in the surface control unit 6 can be all devices or components capable of achieving their own functions in the prior art, and their structures and principles are well known to those skilled in the art, which will not be described here.

[0063] According to the pipe string 100 of the present application, first, thanks to the design and arrangement of the smart valve 3 and other components, the wellbore 5 with liquid loading can use the gas source section 51 as a gas source to complete the gas lifting operation, without the need to increase additional gas sources, gas lifting equipment and processes, thereby reducing the cost and energy consumption of the gas lifting operation and improving the efficiency of the gas lifting operation. Second, through the design and cooperation of the smart valve 3 and the surface control unit 6, the automatic determination of the downhole liquid loading condition and the automatic operation of the gas lifting operation are realized, improving the flexibility, automation level and operation convenience of the gas lifting operation. Third, thanks to the design and use of the packer 2, the gas source section 51 is isolated from other gas-producing sections, avoiding interference between different sections, so that the gas lifting operation can be smoothly realized without significantly affecting the gas production. Fourth, the pipe string 100 can be applied to various types of wells such as horizontal wells, deviated wells and vertical wells, and various working conditions where the gas source section is located at different positions in the well, with a wide range of applications.

[0064] According to the second aspect of the present application, a downhole gas lifting method is provided.

[0065] The downhole gas lifting method uses the pipe string 100 as described above, comprising the following steps:

[0066] 1) determining the liquid loading of the wellbore 5;

[0067] 2) when the amount of liquid loading in the wellbore 5 reaches or exceeds the set opening threshold, opening the smart valve 3 and performing gas lifting operation using the gas source section 51;

[0068] 3) when the amount of liquid accumulation in the wellbore 5 is reduced to or below the set closing threshold, the smart valve 3 is closed, and the gas lifting operation is ended.

[0069] In one embodiment of the present application, the calculation equation for determining the amount of liquid accumulation in the wellbore 5 in step 1) is: W = 3.14*10 -6 *d 2 *(Pc-Pt) / 4pg, wherein W represents the calculated amount of liquid accumulation in the wellbore 5, d represents the inner diameter of the tubing 1, Pc represents the pressure in the annulus between the tubing 1 and the wellbore 5, Pt represents the pressure in the tubing 1, p represents the density of the liquid accumulation in the wellbore 5, and g represents the acceleration of gravity.

[0070] In one embodiment of the present application, the opening threshold and the closing threshold in step 2) and step 3) are empirical values set artificially according to the size of the gas well energy, and the opening threshold and the closing threshold generally gradually decrease with the decrease of the gas well energy.

[0071] In one embodiment of the present application, steps 1), 2) and 3) are automatically performed by the ground control system 6.

[0072] The downhole gas lifting method according to the present application can achieve the technical effects that the tubing string 100 according to the present application can achieve, which will not be described here again.

[0073] In the present application, the specific meanings of "up", "down", "inner", "outer", "middle", "edge" and the like when used to indicate the orientation are as follows: Figure 1 The drawing state of the middle tubing string 100 is taken as the reference.

[0074] Finally, it should be noted that although the present application has been described in detail with reference to the preferred embodiments, various modifications can be made to it and equivalent replacements can be made to the components thereof without departing from the scope of the present application. In particular, each of the technical features mentioned in the various embodiments can be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A gas lift string in a well, comprising: a tubing (1); a pack-off section (2) participating in a pack-off operation of a gas source section (51), comprising no less than one packer; an intelligent control valve (3) configured to be connected to the tubing (1) and located in the gas source section (51); and a sliding sleeve (4) selectively arranged on the tubing (1), wherein the intelligent control valve (3) is configured to enable high-pressure gas in the gas source section (51) to enter the tubing (1) to lift accumulated fluid inside a wellbore (5) out of the well when the intelligent control valve (3) is in an open state. The intelligent control valve (3) comprises a first body (31), a first circulation hole (32) opened on a side wall of the first body (31), and a gas guide cylinder (33) arranged inside the first body (31), a control assembly (34) configured to be able to operate in response to an external instruction is arranged inside the gas guide cylinder (33), a telescopic mechanism (35) is connected above the control assembly (34), and the telescopic mechanism (35) is configured to be able to move to block or expose the circulation hole (32) in response to an instruction of the control assembly (34).

2. The downhole gas lift string of claim 1, wherein: The control assembly (34) comprises a sealing cylinder (341), and a control power supply (342), a motor (343) and a transmission mechanism (344) assembled inside the sealing cylinder (341), the control power supply (342) is configured to be able to realize connection and communication with an issuing device of the external instruction, and sequentially cause the motor (343) and the transmission mechanism (344) to operate, and the transmission mechanism (344) is configured to be able to drive the telescopic mechanism (35) to move.

3. The downhole gas lift string of claim 2, wherein: For a horizontal well, a deviated well or a vertical well in which the gas source section (51) is located at an uppermost section in the wellbore (5), the pack-off section (2) comprises a first packer (21), and the gas source section (51) is packed off by the first packer (21) and a wellhead device.

4. The downhole gas lift string of claim 3, wherein: For a horizontal well, a deviated well or a vertical well in which the gas source section (51) is located at an intermediate section in the wellbore (5), the pack-off section (2) comprises the first packer (21) and a second packer (22), the gas source section (51) is packed off by the first packer (21) and the second packer (22), and a sliding sleeve (4) is arranged on the tubing (1) close to the wellhead side of the pack-off section (2).

5. The downhole gas lift string of claim 3, wherein: For a horizontal well, a deviated well or a vertical well in which the gas source section (51) is located at a lowermost section in the wellbore (5), the pack-off section (2) comprises the first packer (21), the intelligent control valve (3) is arranged at the lowermost end of the tubing (1), a plug configured to close the lower end of the tubing (1) is arranged at the lower end of the intelligent control valve (3), and a sliding sleeve (4) is arranged on the tubing (1) close to the wellhead side of the pack-off section (2).

6. The downhole gas lift string of claim 3, wherein: A surface control section (6) is arranged, and the surface control section (6) is configured to control opening and closing of the intelligent control valve (3).

7. The downhole gas lift string of any one of claims 1 to 6, characterized by: ​ 8. The downhole gas lift string of claim 7, wherein: The surface control unit (6) comprises a control host (61), a first pressure measuring line (62) and a second pressure measuring line (63) respectively extending from the control host (61) to the inside of the tubing (1) and the annulus between the tubing (1) and the wellbore (5), and a cable connecting the control host (61) with the smart valve (3), the control host (61) being configured to automatically control the smart valve (3) to be open or closed by calculating and judging the pressure data fed back by the first pressure measuring line (62) and the second pressure measuring line (63).

9. A downhole gas lifting method using the downhole gas lifting string according to any one of claims 1 to 8, comprising the following steps: 1) judging the accumulation of fluid in the wellbore (5); 2) when the amount of accumulated fluid in the wellbore (5) reaches or exceeds a set opening threshold, opening the smart valve (3) and performing gas lifting operation by using the gas source section (51); 3) when the amount of accumulated fluid in the wellbore (5) drops to or below a set closing threshold, closing the smart valve (3) and ending the gas lifting operation.

10. The downhole gas lift method of claim 9, wherein: The calculation equation for determining the amount of accumulated liquid in the wellbore (5) in the step 1) is: W = 3.14*10 -6 *d 2 *(Pc-Pt) / 4pg, wherein W represents the calculated amount of accumulated liquid in the wellbore (5), d represents the inner diameter of the tubing (1), Pc represents the pressure in the annulus, Pt represents the pressure in the tubing (1), p represents the density of the accumulated liquid in the wellbore (5), and g represents the acceleration of gravity.

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